Self-contained artificial heart

ABSTRACT

A small, self-contained blood pump with integral power source comprising an isotopic thermal source which drives both a Rankine cycle steam engine and a thermoelectric converter which generates electricity to drive a physiologically-responsive beat rate control system, a solenoid-driven feed liquid pump, and a plumonary edema protection system.

United States Patent Purdy Aug. 13, 1974 [54] SELF-CONTAINED ARTIFICIAL HEART OTHER PUBLICATIONS [75] Inventor: David Purdy, lndlana The Development of An lnrapericardial Cardiac Re- 7 Assigneec ARCO Nuclear Company, placement by W. H. Burns et al., Transactions Amephiladelphia, p rican Society for Artificial Internal Organs, Vol. Xll, 1966, pages 272-274. [22] Filed: Dec. 18, 1970 [21] App], No; 99,635 Primary Examiner-Richard A. Gaudet Assistant Examiner-Ronald L. Frinks F 52 us. ca 3/1, 3/1310. 2, 128/1 D, Agent R Ewbank 417/394, 417/468, 60/24, 60/25 51 1m. (:1. A61f 1/24 [57] ABSTRACT [58] Field of Search. 3/1, DIG. 2; 417/394, 395, A Small, self-comalned blood P p wlth Integral 7 321 4 0 4 0 2 25 3; 92 7 power source comprising an isotopic thermal source 128/] D, DIG 3 which drives both a Rankine cycle steam engine and a thermoelectric converter which generates electricity 5 References Cited to drive a physiologically-responsive beat rate control UNITED STATES PATENTS system, a solenoid-driven feed liquid pump, and a plumonary edema protection system. 3,048,l65 8/l962 Norton 3/DIG. 2 o 3,379,191 4/1968 Harvey 3/1 X 18 Claims, 9 Drawlng Figures vnyvvvvm I PATENTEU I 31974 SHEEY 2 0? 6 INVENTOR.

D AVID L. PURDY 8, EM ATTORNEY PAIENIEB I SHEU 3 BF 6 INVENTOR.

o AVID P u R DY BY I ; ATTORNEY PAIENIEBMI 31914 SHEET 6 0F 6 om 5252M; m #6152 E3 mm N ATTORNEY SELF-CONTAINED ARTIFICIAL HEART BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to a single unit mechanical device capable of circulating .blood in the human body in place of a human heart and capable of surgical implantation in the thoracic cavity in a single operation.

2. Description of the Prior Art Previous nuclear powered mechanical heart devices such as the one shown in US. Pat. No. 3,379,191 of Apr. 23, 1968, were comprised of two separate units, one to be implanted in the thoracic cavity and separate power source unit to be implanted in the abdominal cavity with a connecting line to pass the steam generated at the boiler unit of the power source and return the used steam to a condenser and then back to the power source. Another disadvantage of the prior art devices was that the artificial ventricles were mechanically coupled to the recipricating piston and when the piston drew blood into the ventricles, the atrial system tended to collapse under the negative pressure induced therein. Adequate precautions were not taken against pulmonary edema which resulted from continuous pumping of blood to the lungs beyond capacity of the blood vessels therein. Although prior art devices could be set at a selected beat rate, no one has previously conceived of means for varying the beat rate or blood pump output of an implantable artificial heart according to the bodys need for blood as a natural human heart does.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a single unit artificial heart device having an integral energy source and controls adapted to be implanted in the pericardial sac in place of a human heart.

It is a further object ofthis invention to provide a radioisotope powered artificial heart having a Rankine cycle steam engine and a thermoelectric module allowing close simulation of the functions of a.human heart by electrical control of pumping rate and pulmonary to systemic pumping ratio in response to physiological need.

Another object is to provide an artificial heart which is more efficient and longer lasting than previous devices.

Another object is to provide an artificial heart which is lighter than previous devices.

Antoher object is to efficiently and effectively vent isotopic decay by-product helium to the bloodstream surrounding a radioisotope-powered artificial heart.

A further object is to provide an improved means for passing excess heat from thermal energy driven artificial heart'devices directly to the bloodstream.

Another object is to provide an implantable artificial heart which operates effectively without regard to position or attitude of the wearer. Other objects of this invention will become apparent from the description of the invention which follows.

Broadly, the invention is a self-contained artificial heart including a radioisotope source of thermal energy, a thermoelectric module adapted to convert a first portion of said thennal energy into electric power which is used to drive a feedliquid pump and an electronic control circuit adapted to simulate a natural hearts action by varying the pulse and flow rate in response to a physiological variable, and a boiler of a Rankine cycle steam engine adapted to convert a second portion of the thermal energy into mechanical pumping power.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section taken approximately on the line l1 of FIG. 2 of a self-contained artificial heart constructed in accordance with one embodiment of the invention;

FIG. 2 is a cross-section taken on the line 22 of FIG. 1;

FIG. 3 is a fragmentary plan view of the left hand end portion of FIG. I;

FIG. 4 is a diagramatic one half plan view taken on the line 44 of FIG. 2;

FIG. 5 is a part sectional and part elevational view illustrating the piston and cylinder and associated right and left artificial ventricles in compressed position;

FIG. 6 isa circuit diagram of the beat rate and stroke length control system;

FIG. 7 is a circuit diagram of the right ventricle blood inlet valve control system;

FIG. 8 is a circuit diagram of the feedliquid pump control system; and

FIG. 9 is a schematic of the electrical and working fluid flow system.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS Referring to the drawings which show an illustrative embodiment of the blood pump device of the invention, the device 10 contains a source of thermal energy 11 preferrably a radioisotope and most preferably a compound of plutonium A thermoelectric converter 12 is in proximity to the thermal energy source 11 and functions to convert a first portion of the thermal energy from Pu compound 11 to electrical energy. Also in close proximity, preferably surrounding the source of thermal energy, and most preferably surrounding the converter 12, is a monotube boiler 13 which functions to vaporize and superheat the working fluid. The working fluid maybe any one suitable for use in a Rankine cycle engine such as hydrocarbon, halogenated hydrocarbons such as that family of compounds known as the Freons, or water. The working fluid is changed from its liquid to its gaseous state in the boiler 13 by a second portion of the thermal energy and is passed to an expansion zone 14 established by stationary piston 15 and reciprocally movable cylinder head assembly 16 through a solenoid controlled inlet valve 17 in said stationary piston 15. The stationary piston 15 also contains a solenoid-operated exhaust valve 18. The cylinder head assembly 16 moves first away from the piston 15 when the inlet valve 17 is opened and the exhaust valve 18 is closed, and second toward the piston 15 when the exhaust valve 18 is opened and the inlet valve 17 is closed. When the cylinder head assembly 16 is moving away from the stationary piston 15, it compresses an artificial right ventricle l9 and an artificial left ventricle 20 simultaneously to expel blood therefrom by means of a pusher plate member 2121 which is attached to the cylinder head 16 but is preferably not physically attached to the ventricles l9 and 20. When the cylinder head 16 is moving back toward the piston 15, it causes the pusher plate 21-21 to move away from the ventricles 19 and 20, allowing them to expand and allow blood to enter naturally as indicated by arrows 23 and 22 (respectively for ventricles 19 and 20) in FIG. 3; that is, as a result of the pressure in the atrial system and not as a result of the negative pressure which would be cause if the pusher plate 21 were attached directly to the ventricles 19 and 20 and forced them open. When the ventricles 19 and 20 are compressed as shown in FIG. as a result of the force of cylinder head assembly 16, blood is caused to be expelled as indicated by arrows 24 and 25 (respectively for ventricles l9 and 20) in FIG. 3 into both the systemic and the pulmonary systems of the mammal in which the blood pump is implanted.

By transmitting the engine cylinder force directly to the blood, a pulse shape very similar to that of the human heart can be obtained, resulting from the high initial force as gas initially enters the cylinder and rapidly decreasing as the engine cylinder moves. Blood indicated by the arrow 25 from the left artificial ventricle is passed to a connection 26-to the patients aorta while blood 24 from the right artificial ventricle 19 is passed to a specially designed pulmonary artery connection 27 containing an outlet valve 28. The inlet 29 to this right artificial ventricle 19 preferably contains an electromagnetically controlled valve 30 to be described in more detail later in the specification. The aorta connection 26 also contains a valve 31 to prevent backflow of blood in the opposite direction. The left ventricle 20 also contains a blood inlet valve 32 which allows blood 22 only to enter the left ventricle 20.

The aorta connection 26 pulmonary, artery connection 27, left and right artificial ventricles 20 and 19 are constructed of any suitable medical grade material which is compatable with blood and body tissues. Natural and synthetic polymer materials such as polyurethane, dacron, hepranized silastic, and silicon polymers are merely exemplary; the particular material selected does not form a part of the present invention.

A capillary condenser tube 33 is connected to the piston exhaust valve 18 and preferably has an inner surface lined with a fibrous metal wick 34. For example, such a wick-type of capillary lining may be formed from sintered titanium-aluminuni-vanadium alloy. Exhaust vapor entering the condenser tube 33 at 36 (FIG. 9) condenses on the porous wick 34 and fills the wick pores. The condensate flows through the wick 34 to the exit 35 (FIG. 9) of the condenser and then through a subcooler 37 (FIG. 4) to the inlet 38 of the feedliquid pump 39. The condensate is retained in the wick by capillarity regardless of the position or attitude of the heart device. The capillary condenser 33 has a large surface area and rejects heat to an interstitial fluid 43 which in turn rejects its heat to the blood in the ventricles l9 and 20 and maximizes the distribution of heat while minimizing the blood temperature rise. The feedliquid pump 39 is preferably driven by an electrically operated solenoid 40 drivenby an electronic control system shown in FIG. 8 at a constant rate. From the feedliquid pump 39 the working fluid is passed back to the boiler 13 where it is vaporized again.

The availability of the electric power from the thermoelectric module or converter provides for electronic control of various functions of this artificial heart which make it superior to any prior art artificial heart. The thermo electric module 12 is preferably a series of silicon-germanium semi-conductor thermocouples. The thermoelectric converter 12 provides electricity to electrical control circuits (shown in FIG. 6) which control the electromagnetic gas inlet valve 17 and the electromagnetic exhaust valve 18 in the piston 15, which function to control precisely either or both the stroke length and the cycle rate of the movable cylinder head assembly 16. In the preferred embodiment, the electrical control circuit (FIG. 6) is adapted to vary the pulse rate and the stroke length in response to a physiological variable such as blood pressure, variations in which are detected by means of a sensor such as a pressure sensitive transistor thereby varying the rate of pumping of blood in response to the physiological variable, closely simulating the behavior of a natural human heart.

The converter 12 also provides electricity for another electrical control circuit (shown in FIG. 7) which is preferably provided to control an electromagnetic valve 30 at the blood indicated by arrow inlet 29 to the right artificial ventricle l9 and is adapted to control the amount of blood 23 entering the right ventricle 19. A sensor (not shown) of pulmonary blood pressure is provided which signals the control circuit (FIG. 7) when the pulmonary blood pressure risesabove a predetermined level and causes the electromagnetic valve 30 to be closed until the pulmonary blood pressure drops to an acceptable level. Pulmonary edema is thereby effectively prevented because of the artificial hearts adaptability to change the systemic system to pulmonary system pumping rate ratio.

Since the rate of blood pumping and hence flow of working fluid through the cylinder may be varied, and the feedliquid pump preferably operates at a constant rate, there will be excess vapor during the major portion of normal activity and during periods of low blood flow power demands. A relief valve (FIG. 9) is provided to release excess vapor from the boiler superheater 46 into the condenser 33 at 36 at a predetermined pressure.

The source of thermal energy 11 previously mentioned is preferably compound of a Pu isotope and is shielded preferably by a platinum capsule 41 having an absolute filtered vent 42 (FIG. 1) to duct helium generated by said isotope 11 during the course of this decay directly into the interstitial fluid 43. The helium permeates the silastic covering 44 into the bloodstream. A microsphere fuel form is coated first with thoria and then with platinum-rhodium to form a ductile mass which withstands any credible impact as well as fire or any credible accident.

An internal cylindrical bellows 47 and an external cylindrical bellows 48 (FIGS. 1 and 2) are provided, one end of each being welded to the movable cylinder head 16 and the other end of each being welded to a stationary member 49 which is affixedly attached to the piston 15. The internal bellows 47 forms a hermetic seal to prevent any possible working fluid escape and to vent any vapor leakage past the cylinder 14 directly to the condenser 33. In the preferred embodiment, there is provided a xenon-filled annular chamber defined by bellows 47 and 48. Much of such annular chamber is oocupied by thermally insulating, slidably interfitting Min-K cylindrical cans 50 and 51 which act as thermal insulators. Surrounding this annulus is the external bellows 48 which provides a hermetic seal for xenon 52 containment. Xenon 52 provides the dual function of lowering the thermal conduction of the annulus and ventricles 19 and 20, thereby expelling the blood. At

the completion of the pump stroke the pressure in the cylinder will have dropped and the exhaust valve 18 will open for at least a portion of the return stroke.

DESCRIPTION OF CIRCUITRY The artificial heart is controlled by circuitry responsive to some physiological function such as the average blood pressure, filtered to eliminate the variations from beat to beat. In FIG. 6, dotted lines enclose certain electronic functions, which have inter-relationships shown by the schematic diagram. A variable voltage signal indicative of the variations in blood pressure is regulated by the Right Atrial Pressure Sensor unit, there being a suitable transducer in the right atrium. The human body is thus a significant participant of the feedback loop.

Particular attention is directed to the feature whereby this average blood pressure signal varies both the stroke and the rate of the artificial heart, thus simulating the normal hearts capacity for increasing both the volume per beat and the rate of the pumping action. That portion of FIG. 6 within the dotted lines identified as Rate Control is a multivibrator, the rate of which is controlled by the average blood pressure. The Gas Inlet Control is an emitter coupled monostable vibrator, the pulse width of which is varied by the average blood pressure. The train of thus regulated pulses actu ates a driven circuit identified as a Gas Inlet Switching Network whereby the gas inlet valve 17 solenoid is energized to control both the stroke and the rate of the reciprocating cylinder head assembly 16. The exhaust valve 18 is regulated by a solenoid energized through a Gas Exhaust Switching Network driven by the signal from the Gas Exhaust Control, the frequency of the pulses being the complimentary output of the Rate Control regulated by the feedback signal from the human body through the Right Atrial Pressure Sensor.

The current from the thermoelectric converter 12 energizes the circuits of FIGS. 6, 7, and 8. Within each set of dotted lines, any transistor described as a second transistor is the one on the right, the leftward transistor being called the first transistor.

The reciprocation rate of the cylinder head assembly 16 is controlled by the rate at which the inlet valve 17 is opened. A less than maximum stroke length is achieved by shortening the duration of the opening of the inlet valve 17. The exhaust valve 18 is electrically actuated toward the open position during at least some portion of the cycle when the intake valve is not so actuated.

The gas inlet valve solenoid is controlled by a Gas Inlet Switching Network." A Gas Inlet Control is an emitter-coupled monostable vibrator whose pulse is triggered by the train of pulses from the Rate Control, the pulse width being varied by the signal from the Right Atrial Pressure Sensor. Thus, when the body sends back more blood toward the heart, the pumping capacity is increased in part as a result of increasing the stroke by increasing the pulse width.

The Gas Inlet Switching Network is a driver circuit comprising a first and second transistor. A positive current is directed through a diode, a resistor, the solenoid coil for the inlet valve 17 and the collector and emitter of the second transistor. The base of the second transistor is controlled by the emitter signal from the first transistor developed across a resistor voltage divider. The emitter of the second transistor is also connected by two parallel capacitors to the collector through the solenoid winding in the valve 17 for the gas inlet. A diode in parallel with the solenoid winding for the valve 17 of the gas inlet serves to prevent any adverse effects from the intermittent potential in the solenoid. In the operation of the Gas Inlet Switching Network, the low power signal from the Gas Inlet Control regulates both the frequency and duration of valve opening, and the switching network unit controls the flow of the higher power current to the solenoid of the valve 17.

The Gas Inlet Control is an emitter-coupled monostable vibrator and includes two common emitter con nected transistors, the emitters being maintained above ground by a resistor to ground. The base of a first transistor of the Gas Inlet Control isconnected through a resistor to the collector of the second transistor, which provides an output signal from the Gas Inlet Control. The collectors of the first and second transistors of the gas inlet control are connected through their respective resistors to a positive potential. The signal on the collector of the first transistor is coupled to the base of the second transistor through a capacitor. The pulse width is increased when the heart rate is increased because the Gas Inlet Control is modulated by the output signal of the right atrial pressure sensor. For example, such atrial signal can be connected through a resistor to the base of the second transistor.

The Rate Control unit is an R-C coupled common emitter multivibrator. The base of each transistor is connected by a capacitor to the collector of the other transistor and by a resistor to the positive signal from the Right Atrial Pressure Sensor. Similarly, the collector of each transistor is connected through a resistor to such positive signal from the Right Atrial Pressure Sensor."

The operation of the Rate Control unit can be clarified by noting that a positive signal from the Right Atrial Pressure Sensor is converted by the multivibrator to two trains of pulses at a right of the general magnitude of a natural heart beat, the pulses from one side of the multivibrator being directed to the Gas Exhaust Control and the other train of pulses from the other side of the multivibrator being directed to the Gas Inlet Control. The frequency of the multivibrator increases when the body needs more blood circulation as communicated by the positive signal from the Right Atrial Pressure Sensor.

The Right Atrial Pressure Sensor includes a transducer responsive to the pressure in the right atrium, such transducer being associated with the base of the transistor in such unit. A voltage divider between the positive terminal of the source of electrical potential and ground provides a controlled voltage to the base. The emitter of the transistor is connected by a resistor to ground. The collector is connected by a resistor to the positive terminal of the source of electrical potential. The output signal at the collector is coupled to supply the positive potential for the multivibrator by an isolating diode in series with a resistor. A capacitor is connected between such resistor and ground. Such association of the electronic components in the unit designated as the Right Atrial Pressure Sensor" provides a filtered signal (the beat to beat variations being rejected) which is a smoothly varying positive signal indicative of average atrial pressure, and this signal regulates the variations of both the Rate Control" unit and the Gas Inlet Control for controlling both the rate and stroke of the reciprocations of the cylinder head assembly 16. In this manner, the entire system closely simulates the response of a natural heart to right atrial pressure.

The Gas Exhaust Control is similar in configuration and operation to the Gas Inlet Control. A signal consisting of a train of pulses from the multivibrator is applied to the base of the first transistor. The bias, however, is derived directly from the positive potential source, rather than from the positive output of the Right Atrial Pressure Sensor because the working fluid can flow through an open exhaust valve during the same fraction of a cycle without regard to whether the inlet valve was long open for a full stroke or a shorter time for a partial stroke.

The Gas Exhaust Switching Network includes a transistor, the base of which is connected through a resistor to ground. The solenoid coil operating the gas exhaust valve is connected in series with the collector to the positive potential source. A diode bypasses the solenoid coil of the gas exhaust valve 18 to protect the transistor from a voltage spike when the solenoid current is interrupted.

In the operation of the circuitry of FIG. 6, the pressure sensor at the right atrium provides a positive signal upon which is impressed the collector voltage developed by the base current generated by the right atrial pressure. The pulse rate of the Rate Control is controlled by the voltage of the Right Atrial Pressure Sensor to provide a train of pulses to the Gas Inlet Control and the Gas Exhaust Control. The respective gas inlet and exhaust switching networks are operated by their controls so that the valves are actuated at rates determined by the pressure in the right atrium, and the inlet switching network is additionally controlled to narrow the proportion of maximum pulse width sent to the gas inlet valve solenoid coil except when a predetermined high pressure of the right atrium is exceeded. Thus, as the body sends back blood to the heart at a greater rate, the hearts pumping capacity is increased by increasing both the stroke of the cylinder head assembly 16 and the frequency or number of strokes per minute.

FlG.7 depicts a Pulmonary Edema Protector" and is effectively a blood switching system which prevents the flow of blood to the lungs during those periods when the average pulmonary blood pressure is excessive. When the pulmonary, arterial, average pressure rises above a predetermined value, the Schmidt trigger changes state and closes blood inlet valve 30 by which the blood would flow to the lungs through the right ventricle. The Pulmonary Edema Protector includes two transistors, the emitters of which are connected together and maintained above ground potential by a resistor. Each collector is connected through a resistor to the positive terminal, and the bases are each biased by a resistor to ground. The input signal is coupled through a resistor from the Pulmonary Arterial Pressure Sensor" to the base of the first transistor, and the output signal from the collector of the first transistor is coupled by a resistor to the base of the second transistor.

The signal at the collector of the second transistor of the Pulmonary Edema Protector is coupled through a resistor to the base of the single transistor in the Blood Inlet Switching Network, a circuit similar to the Gas Exhaust Switching Network described above with respect to FIG. 6.

In operation, the openingor closing of the right ventricle blood inlet valve 30 is controlled by the Blood Inlet Switching Network." Such valve is closed in re sponse to any signal from the Pulmonary Edema Protector, which signal is sent only during the brief moments when the pulmonary arterial pressure exceeds the predetermined limit. The Pulmonary Edema Protector protects the system so that the lungs are protected from blood circulation rates greater than the lungs can at that moment satisfactorily process, even when the flow of blood back to the heart might suggest a greater circulation rate. Thus, the inlet valve 30 for the blood for the right ventricle is closed during those moments appropriate for responding to the ability of the lungs to process such rate of blood circulation, but is open much of the time.

In FIG. 8, the voltage source is conducted through a zener diode voltage stabilizer to a feed liquid Pump Rate/Duration Control, a multivibrator comprising two transistors of opposite conductivity type. The emitter of the first transistor is connected directly to the positive potential. The collector of the second transistor is connected by a resistor to such positive potential. The collector of the first transistor is connected through a resistor, and the emitter of the second transistor is connected directly to ground. The bases of the two transistors are interconnected by a symmetrical network, each including a base-to-collector resistor and a capacitor and resistor in series between the base of one transistor and the collector of the other. The feed liquid Pump Switching Network is essentially of the same configuration and operation as the Gas Inlet Switching Network of FIG. 6.

In the operation of the circuitry of FIG. 8, the oscillator of the rate control unit provides a train of pulses of controlled duration which actuate the heavy duty switching of the switching network unit to energize the solenoid 40 to operate the pump 39 at a predetermined constant rate. By appropriate choice of the resistors in the symmetrical base-collector network of the feed liquid pump rate/duration control, the relative time between adjacent pulses as well as the pulse duration can be readily controlled.

The embodiments of ny invention described in great detail are merely illustrative of the invention. Certain obvious modifications might eventually be apparent to those skilled in this art without departing from the spirit and scope of my invention as set forth in the claims.

What is claimed is:

1. An implantable artificial heart having a housing of a size to fit within the chest cavity after removal of a major portion of the natural heart, said housing enclosa radioisotope thermal energy source;

a thermoelectric converter positioned to convert a first portion of the thermal energy of the radioisotope to electrical energy;

a Rankine cycle engine, said engine having a working fluid boiler tube positioned to absorb a second portion of thermal energy of the radioisotope, said engine having a stationary piston and a reciprocally movable cylinder head assembly;

artificial left and right ventricles arranged so that when said cylinder head assembly moves in one direction, said ventricles are compressed to expel blood therefrom; and

electrical control means energized by said thermoelectric converter, said electrical control means regulating at least one of the rate and stroke of reciprocation of said cylinder head assembly.

2. The device of claim 1 wherein said engine contains:

a condenser tube extending from a piston exhaust valve to a feedliquid pump, said condenser tube comprising capillary internal surfaces.

a feedliquid pump driven by a solenoid adapted to I pump working liquid to said boiler tube, and

said boiler tube at least partially surrounding said thermal energy source said boiler tube being adapted to convert a working fluid from liquid to gas.

3. The device of claim 1 further including a pusher plate assembly reciprocatingly actuated by said cylinder head assembly adapted to simultaneously compress both said left ventricle and said right ventricle.

4. The device of claim 1 wherein said thermoelectric converter is comprised of a series of silicongermanium semiconductor thermocouples and is disposed adjacent to said source of thermal energy.

5. The device of claim 1 wherein said isotope is a P11 compound and is shielded by a platnium capsule.

6. The device of claim wherein said capsule contains an absolute filtered vent to conduct helium generated by said isotope directly into an interstitial fluid and thereafter into the bloodstream.

7. The device of claim 1 further including sensing means for sensing a physiological variable, electrical control circuits powered by electricity from said thermoelectric converter and adapted to electronically regsenses blood pressure, and wherein there are electronic means converting the signal to a filtered smoothly varying potential indicative of average blood pressure, said potential being applied to a multivibrator to regulate the oscillation frequency, and to a control for the working fluid inlet valve to regulate the width of pulse and duration of inlet valve opening.

10. The device of claim 1 in which the electrical control means powered by electricity from said thermoelectric converter includes sensing means to determine average pulmonary blood pressure, an electromagnetic valve at the blood inlet to the right artificial ventricle adapted to control the time when blood may enter said right ventricle, said control means being adapted to hold said valve closed when said average pulmonary blood pressure is sensed to be above a predetermined level.

11. The device of claim 2 wherein said condenser tube is a tube having an inner surface lined with metal wick which is adapted to condense working fluid gas to liquid and conduct capillary flow of condensate regardless of attitude of device.

12. The device of claim 11 wherein said metal wick has a composition of sintered titanium-aluminumvanadium alloy.

13. The device of claim 2 wherein said feedliquid pump solenoid is controlled by an electrical circuit which is adapted to reciprocate a piston in said pump at a controlled rate so as to supply working liquid to said boiler tube at a controlled rate.

14. The device of claim 2 further including a flexible cylindrical bellows exterior to said piston adapted to prevent working fluid from leaking from said cylinder and to direct any leakage of working fluid tov said condenser.

15. The device of claim 14 further including a second flexible bellows exterior to and concentric with the first bellows, the annular inter-bellows zone containing xenon providing a relative gas pressure adapted to compensate against adverse effects from varying pressures affecting said cylinder head assembly.

16. The device of claim 2 further including a condenser and a relief valve direction excess gaseous working fluid from said boiler tube to said condenser, said valve being adapted to release excess gas from said boiler at times when the'pressure in said boiler exceeds predetermined limits.

1?. A self-contained implantable artificial heart comprising:

a compound of Pu isotope source of thermal ena thermoelectric converter positioned adjacent said isotope and adapted to convert a first portion of said thermal energy into electric power;

an electric solenoid driven feed pump adapted to force liquid working fluid into a boiler tube;

a boiler tube surrounding the combination of said isotope source and said thermoelectric converter adapted to boil said liquid working fluid received from said feed pump by converting a second portion of said thermal energy, said boiler tube directing resultant vapor of said working fluid toward a vapor inlet valve;

a Rankine cycle working fluid engine driven by the hot working fluid vapor, said engine having a reciprocally movable cylinder head assembly;

an electromagneticallyoperated inlet valve for vapor of the working fluid adapted to allow vapor to pass from said boiler into an expansion zone;

an electromagnetically operated vapor exhaust valve adapted to allow vapor to pass out of said expansion zone;

a low pressure capillary condenser adapted to condense vapor to liquid working fluid and to reject condensate heat into an interstitial fluid, said liquid to fit within the chest cavity after removal of a major portion of the natural heart.

18. The device of claim 17 wherein means adapted to sense a physiological variable actuate electrical control means adapted to vary the opening and closing of said inlet and exhaust valves, thereby modifying the blood circulation rate in response to changes in said physiological variable.

UNITED STATES PATENT OFFICE CERTIFICATE 9F CORRECTEQN Patent No. 3,828,371 Dated August 13, 197

Inventor(g) David L. Purdy Ii: is certified that error appears in the above-identified patent and that said Letters Patent are hereby confected as shown below:

Claim 16, line '2, "direction" should read directing Signed and sealed this 26th day of November 1974.

(SEAL) Agcest:

.McoY M'.'c1BsoN 312.. c." MARSHALL DANN Attesting Officer Comis sionep of Patents I F ORM PO-IDSO (1069) 

1. An implantable artificial heart having a housing of a size to fit within the chest cavity after removal of a major portion of the natural heart, said housing enclosing: a radioisotope thermal energy source; a thermoelectric converter positioned to convert a first portion of the thermal energy of the radioisotope to electrical energy; a Rankine cycle engine, said engine having a working fluid boiler tube positioned to absorb a second portion of thermal energy of the radioisotope, said engine having a stationary piston and a reciprocally movable cylinder head assembly; artificial left and right ventricles arranged so that when said cylinder head assembly moves in one direction, said ventricles are compressed to expel blood therefrom; and electrical control means energized by said thermoelectric converter, said electrical control means regulating at least one of the rate and stroke of reciprocation of said cylinder head assembly.
 2. The device of claim 1 wherein said engine contains: a condenser tube extending from a piston exhaust valve to a feedliquid pump, said condenser tube comprising capillary internal surfaces. a feedliquid pump driven by a solenoid adapted to pump working liquid to said boiler tube, and said boiler tube at least partially surrounding said thermal energy source said boiler tube being adapted to convert a working fluid from liquid to gas.
 3. The device of claim 1 further including a pusher plate assembly reciprocatingly actuated by said cylinder head assembly adapted to simultaneously compress both said left ventricle and said right ventricle.
 4. The device of claim 1 wherein said thermoelectric converter is comprised of a series of silicongermanium semiconductor thermocouples and is disposed adjacent to said source of thermal energy.
 5. The device of claim 1 wherein said isotope is a Pu238 compound and is shielded by a platnium capsule.
 6. The device of claim 5 wherein said capsule contains an absolute filtered vent to conduct helium generated by said isotope directly into an interstitial fluid and thereafter into the bloodstream.
 7. The device of claim 1 further including sensing means for sensing a physiological variable, electrical control circuits powered by electricity from said thermoelectric converter and adapted to electronically regulate at least one of the cycle rate and cylinder stroke length of the reciprocally moving cylinder head assembly in response to said physiological variable to actuate a signal feed back means to the control circuits, there being an electromagnetic working fluid inlet valve and an electromagnetic working fluid exhaust valve regulated by said control circuits.
 8. The device of claim 7 wherein said electrical control circuits have means adapted to vary both pulse rate and cylinder stroke length.
 9. The device of claim 8 wherein said sensing means senses blood pressure, and wherein there are electronic means conveRting the signal to a filtered smoothly varying potential indicative of average blood pressure, said potential being applied to a multivibrator to regulate the oscillation frequency, and to a control for the working fluid inlet valve to regulate the width of pulse and duration of inlet valve opening.
 10. The device of claim 1 in which the electrical control means powered by electricity from said thermoelectric converter includes sensing means to determine average pulmonary blood pressure, an electromagnetic valve at the blood inlet to the right artificial ventricle adapted to control the time when blood may enter said right ventricle, said control means being adapted to hold said valve closed when said average pulmonary blood pressure is sensed to be above a predetermined level.
 11. The device of claim 2 wherein said condenser tube is a tube having an inner surface lined with metal wick which is adapted to condense working fluid gas to liquid and conduct capillary flow of condensate regardless of attitude of device.
 12. The device of claim 11 wherein said metal wick has a composition of sintered titanium-aluminum-vanadium alloy.
 13. The device of claim 2 wherein said feedliquid pump solenoid is controlled by an electrical circuit which is adapted to reciprocate a piston in said pump at a controlled rate so as to supply working liquid to said boiler tube at a controlled rate.
 14. The device of claim 2 further including a flexible cylindrical bellows exterior to said piston adapted to prevent working fluid from leaking from said cylinder and to direct any leakage of working fluid to said condenser.
 15. The device of claim 14 further including a second flexible bellows exterior to and concentric with the first bellows, the annular inter-bellows zone containing xenon providing a relative gas pressure adapted to compensate against adverse effects from varying pressures affecting said cylinder head assembly.
 16. The device of claim 2 further including a condenser and a relief valve direction excess gaseous working fluid from said boiler tube to said condenser, said valve being adapted to release excess gas from said boiler at times when the pressure in said boiler exceeds predetermined limits.
 17. A self-contained implantable artificial heart comprising: a compound of Pu238 isotope source of thermal energy; a thermoelectric converter positioned adjacent said isotope and adapted to convert a first portion of said thermal energy into electric power; an electric solenoid driven feed pump adapted to force liquid working fluid into a boiler tube; a boiler tube surrounding the combination of said isotope source and said thermoelectric converter adapted to boil said liquid working fluid received from said feed pump by converting a second portion of said thermal energy, said boiler tube directing resultant vapor of said working fluid toward a vapor inlet valve; a Rankine cycle working fluid engine driven by the hot working fluid vapor, said engine having a reciprocally movable cylinder head assembly; an electromagnetically operated inlet valve for vapor of the working fluid adapted to allow vapor to pass from said boiler into an expansion zone; an electromagnetically operated vapor exhaust valve adapted to allow vapor to pass out of said expansion zone; a low pressure capillary condenser adapted to condense vapor to liquid working fluid and to reject condensate heat into an interstitial fluid, said liquid working fluid being directed from said condenser to said feed pump; left and right artificial ventricles adapted to be simultaneously compressed by said reciprocating cylinder head assembly and to expel blood when compressed, said interstitial fluid having heat transfer relationship with said artificial ventricles; and a housing enclosing said source, converter, pump, boiler tube, engine, inlet valve, exhaust valve, condenser, and ventricles, said housing being of a size to fit within the chest cavity afTer removal of a major portion of the natural heart.
 18. The device of claim 17 wherein means adapted to sense a physiological variable actuate electrical control means adapted to vary the opening and closing of said inlet and exhaust valves, thereby modifying the blood circulation rate in response to changes in said physiological variable. 